1. Field of the Invention
The present invention relates generally to cleaning of printing equipment, and more particularly to a chemical composition and method for cleaning dried ink or other dried or hardened substances from an anilox roller utilized in a flexographic printing process.
2. Description of the Related Art
The flexographic printing process or flexography is a process of direct rotary printing of images onto an elongate moving web of material. The process is typically utilized for product packages and containers in many different industries.
Anilox rollers utilized in the flexographic printing process have evolved considerably over the years. Anilox rollers typically come in three types of constructions. The first is a ceramic coating disposed over a knurled surface on a metal cylinder, the second is a chrome-plated surface over a knurled surface of a cylinder, and the third is a laser engraved ceramic surface on a cylinder. In each construction, a plurality of small or microscopic pockets or cells are formed in the coating material of the cylinder in order to carry the ink, adhesive or other coating material from the reservoir to the printing plate cylinder and then to the web. The size of the cells determines how much material each cell will carry. The anilox roller rotates and contacts the plate cylinder transferring the material in the cells to the plates. The engraving process for the cells can create different diameters, depths, shapes and placement angles of cells in order to meet the needs of a particular printing or other process.
Chrome and ceramic coated engraved knurled anilox rollers typically can only have about 500 cells per inch because of the limitations of the technology for forming such a roller. Most printing requirements for today's industries require highly precise image and fluid transfer for which the coated knurled engravings are not well suited. Therefore, the laser engraved ceramic rollers offer many advantages over the other two types of anilox rollers. The cells of a laser engraved anilox roller can be formed having a density upwards of 1200 cells per inch with highly precise control of the shape, depth, size and steepness of the cell walls not capable in other anilox roller constructions. The depth and therefore volume of each laser engraved cell can be significant although the actual diameter or size of the cells can remain very small.
The laser engraved anilox rollers also offer much better durability than these other types of anilox rollers. However, the cost of such rollers is significantly greater because of the high precision manufacturing process necessary to produce the ceramic coated anilox roller. Another significant problem with the anilox rollers is the difficulty in cleaning dried ink or other dried or hardened substance residue from the surface and cells of the roller. This difficulty is caused by the very small microscopic size of the cells and the greater depth to which they are formed into the ceramic surface of the roller. Dried ink or other substances plugs the cells and is very difficult to remove from the anilox roller. The ink or material film flow quality is significantly decreased if an anilox roller is dirty and has clogged or plugged cells because the precision and volume of ink or other material transferred from the reservoir to the plate cylinder is reduced or altered. The metering function of the roller is thus inhibited. Dried ink can occur in all of the cells of the roller or only a portion of the cells depending upon the particular printing process being run. However, any dried ink or other substance occurring in any part of the roller surface causes reduced print quality and ink delivery.
There are a number of known methods and apparatuses utilized to clean anilox rollers. Some of these methods are quite effective while some methods are not. However, the effective methods as well as most of the ineffective methods are very costly, time consuming, require machine downtime and can cause damage to the anilox rollers.
For example, there are ultrasonic cleaners available whereby one or more anilox rollers are partially or completely submerged in a tank containing a highly caustic cleaning fluid. High frequency sound waves are generated in the caustic liquid medium to create microscopic air bubbles that implode on impact with the cells and the cell walls. The implosions force the caustic fluid into the cells to remove dried ink and other substance residue. This type of cleaning system is extremely expensive and is very time consuming. The ultrasonic cleaning equipment also requires its own maintenance, storage and upkeep. The caustic cleaning fluid requires special handling and storage and also requires time consuming and expensive precautionary safety measures be taken during the cleaning process. The use of the equipment requires that the anilox rollers be removed from the flexographic printing machine in order to be cleaned thus creating down time for the machine.
High pressure cleaning systems are also sometimes utilized wherein an anilox roller is placed in a stream of a media ejected from a device at high pressure. The media can be a particle media such as small microscopic plastic particles or a sodium bicarbonate or baking soda specially designed to clean anilox rollers. The media can also be a cleaning liquid or fluid wherein jets or nozzles create an overlapping spray pattern impacting the anilox roller surface. Sometimes the cleaning liquid or fluid is heated to further facilitate cleaning. In some media blast systems, the roller is entirely submerged in the fluid media. Alternatively, some pressure wash systems rotate the roller in an ambient environment whereby a cleaning solution is ejected from nozzles toward the surface of the roller. In this type of system the rollers are not submerged in the cleaning media. Fluid pressure wash systems are less expensive in comparison to other hard media blast systems and when compared to ultrasonic systems. However, the media blast systems and the pressure wash systems are still relatively expensive and require maintenance, storage and upkeep of the equipment as well. Significant downtime of the flexographic printing machine also is necessary since the roller must typically be removed from the machine to be cleaned. There are a few media blast machines available that can attach directly to the flexographic press in order to clean the anilox roller on press. However, this type of machine must be attached and removed for each cleaning and is very cumbersome and expensive to operate and maintain. These machines also incorporate a large, high power vacuum or suction system to collect all of the media. The suction system is also very cumbersome and expensive.
Some cleaning systems utilize a pressurized vapor injection cleaning system wherein the rollers are placed in a stream of a vapor chemical composition. This type of system can be utilized directly on the flexographic machine because very little if any liquid is involved in the cleaning process. This system is fairly inexpensive and portable although again it requires maintenance and storage of the cleaning equipment and requires purchase and storage of the chemical vapor product as well. This type of system is not effective for all types of inks and coating materials and typically has not proven effective for heavy industrial printing processes where heavy and continuous cleaning is required for the anilox rollers.
Another type of system for cleaning anilox rollers involves utilizing the ink reservoir of the flexographic press for cleaning the cells of the anilox roller. This type of system is utilized where the ink is flushed out of the system and then a cleaning solution is replaced in the reservoir and utilized to clean out the cells. This type of system is relatively recent, expensive, and fairly ineffective at removing deeply embedded materials within the cells. A risk exists of not flushing out all of the cleaning solution from the system and then contaminating the subsequently run printing process. This type of self-contained system also requires significant machine downtime.
Manual cleaning is often utilized and even recommended for quick cleaning of anilox rollers. The manual cleaning process involves utilizing a wire brush for agitating ink on the surface and within the cells of the anilox roller. The brush is utilized along with a water based detergent or solvent based cleaner. The types of brushes typically utilized are brass or stainless STEEL bristle brushes wherein the stainless brushes are always utilized for ceramic rollers. This type of cleaning process is very messy, is very time consuming, can damage the ceramic coating if the wrong brush is used, and is limited in its effectiveness for the laser formed ceramic cells of modern anilox rollers. Most times the diameter of the brush bristles is much larger than the diameter of the cells and therefore the material deep within the cells cannot be readily dislodged.
All of these methods usually require removal of the anilox roller from the press prior to cleaning. Some rollers are on the order of sixty inches long or longer and can weigh upwards of a half a ton. A crane or hoist is often used to remove the larger rollers from the press and transport them to the cleaning apparatus or station. The removal is time consuming and requires significant downtime of the press. Manufacturers often recommend keeping a second replacement roller around for this very reason. However, some of the larger rollers can cost tens of thousands of dollars each. The ceramic surface of an anilox roller is very wear resistant and durable. However, the ceramic is also brittle and can be easily damaged upon impact with an object. Each removal of a roller for cleaning therefore also raises a risk of permanently damaging the roller surface.
Another commonly utilized method for cleaning anilox rollers is chemical cleaning whereby relatively harsh chemicals are utilized such as solvents, acids and common strong household cleaners which dissolve or rewet the ink or other substances lodged within the cells. Chemical cleaning, as with virtually all cleaning methods first requires rinsing off or initially wiping the anilox roller to remove most of the wet ink or other substance from the last press run. Then the solution is applied and the anilox roller is wiped to completely cover the surface of the roller. The chemical compositions also require a dwell time so that the composition sits for a period of time on the rollers to react with the deeply embedded and dried substance plugging the cells. The anilox roller is then wiped down with the composition in order to clean the surface. A rinsing process must then be undertaken to remove all of the caustic chemical materials from the surface of the anilox roller as well as from the cells in order to prevent any unwanted residue from fouling up a subsequent print process. A drawback with this type of method is that the rolls must again be removed from the flexographic printing machine so that the chemicals do not contaminate any other portion of the processed components. A further drawback is that this method requires time consuming steps including removing the roller from the press, quick cleaning most of the wet ink from the last print job, applying the chemical composition, letting it sit for a period of time, wiping the roller to clean it, cleaning the chemical from the roller, rinsing the roller with water, and replacing the roller on the press. Another drawback is that this type of cleaning has been found to be ineffective for deeply embedded and dried ink from within the cells of the roller. The advent of the much more expensive and time consuming cleaning methods discussed above are a result of the ineffectiveness of these chemical solution cleaning methods.